1. Field of the Invention
The present invention relate to a method of preparing a tin-silver (Sn—Ag) alloy plating solution, and particularly, to a method of preparing a Sn—Ag alloy plating solution and the plating solution thereby, wherein the method may increase current efficiency and maintain a desirable plating film by eliminating impurities from methanesulfonic acid, which is a base material, in the preparation of methanesulfonic acid tin and methanesulfonic acid silver through an electrolytic process.
2. Description of the Related Art
In general, plating a product or parts of the product may be a necessary process applied to most of the industrial fields. Specifically, the plating may be a significant factor to determine the quality and productivity of mass-produced products in semiconductor manufacturing sites where a light, thin, short, and small product is desirable. Purification technique, thus, may be required to prevent contamination and increase purity of a plating solution by eliminating impurities contained in the plating solution. For example, Korean Patent Publication No. 2005-0092132 entitled “tin-containing plating bath” and Japanese Patent Publication No. 2001-64249 entitled “purification of alkanesulfonic acid” disclose related technologies.
In one working example, the Korean Patent Publication No. 2005-0092132 discloses the tin-containing plating bath that contains (a) a first soluble tin salt or a mixture of the first soluble tin salt and at least one soluble salt selected from the group consisting of copper salt, bismuth salt, silver salt, indium salt, zinc salt, nickel salt, cobalt salt, and antimonial salt, and (b) tin containing at least one aliphatic sulfonic acid selected from the group consisting of alkanesulfonic acid and alkanolsulfonic acid, wherein the aliphatic sulfonic acid may be purified aliphatic sulfonic acid that contains less than a small amount of sulfur compounds, as impurities, including a compound having sulfur atoms with an oxidation number of +4 or less in a molecule and a compound having sulfur atoms and chloride atoms in a molecule. Thus, a tin plating film or a tin alloy plating film that may have a desirable reflow property and exterior will be formed thereby.
In another working example, the Japanese Patent Publication No. 2001-64249 discloses a purification method. The purification method may include at least one step of bringing aqueous alkanesulfonic acid solution into contact with alkaline anion exchange resin, wherein the method may be performed to purify alkanesulfonic acid to reduce a content of sulfuric acid and, additionally, a content of anion other than alkansulfonate ion contained therein, and, specifically, wherein the method may be performed to reduce the content of the sulfuric acid. Thus, the reduction in the content of the sulfuric acid in the alkanesulfonic acid may be achieved by bringing the aqueous alkanesulfonic acid solution into contact with the alkaline anion exchange resin.
However, various substances including chloride ion, in addition to sulfur compounds, may be used when synthesizing a commercially available methanesulfonic acid. Moreover, the chloride ion may adversely affect a structure of a plating film.